Therapeutic substances are often delivered by subcutaneous injection. One common device used to facilitate the delivery of such substances is a subcutaneous injection port. Subcutaneous injection ports typically include a housing with a soft tubular cannula and an apparatus for delivering a therapeutic substance to the cannula. To use such a port, a puncturing device such as a rigid needle is used to place the soft cannula in the subcutaneous tissue. The rigid needle is then withdrawn and the cannula and housing are left at the infusion site. A therapeutic substance may then be introduced through the cannula. This type of subcutaneous injection port may be left in a patient for several days. Examples of subcutaneous injection ports are disclosed in U.S. Pat. No. 6,074,371 to Fischell, and U.S. Pat. No. 6,017,328 to Fischell, which are hereby incorporated by reference in their entirety.
A subcutaneous injection port may be used to deliver a bolus of medicine with a syringe. A subcutaneous injection port suitable for use with a syringe is disclosed in U.S. Patent Publication No. 2004/0006316 A1 to Patton, which is hereby incorporated by reference in its entirety.
One problem that may occur when injecting therapeutic substances into a subcutaneous injection port with a syringe is misalignment between the cannula of the syringe and the injection port. If there is too much misalignment, the injection port may be damaged or improper dosages may be delivered. Furthermore, a user may completely miss the injection port, and accidentally stick themselves with the cannula.
Accordingly, there is a need for an improved apparatus for delivering therapeutic substances into a subcutaneous injection port.